The present invention relates to the separation or concentration of solid materials suspended in a fluid medium and, more particularly, to novel methods and apparati for filtering suspended solid materials at high volume and efficiency without blinding or plugging the filter material.
Conventional filtration techniques for filtering solid particles such as cells, macromolecules (e.g., proteins), or other microsized solid materials which may be suspended in a fluid media utilize a sheet-like membrane or tubule having pores which are impermeable to the particle material. Such techniques strive to maximize the surface area of the selected filter material in order to maximize the volume of fluid which can be filtered before the pores of the surface of the membrane filter become completely filled with particles and thus blinded by the solid material. Prior efforts to obviate membrane blinding have attempted to maintain the solids containing fluid in some sort of tangential flow pattern during the filtration process. The various hardware and methodology employed however are inefficient, cumbersome, expensive to manufacture and eventually result in blinding of the surface of the filter membrane over time in any event.
Other techniques employ a generally cylindrical-shaped filter which rotates at high speeds within a sealed housing. These devices rely on high shear forces to increase the tangential flow patterns that are normally required to prevent membrane fouling. The degree of concentration of the solid material is limited since the high shear rate also tends to mechanically damage the suspended particles. In the case of mammalian or plant cells, the shear forces tend to lyce the cell wall, thereby destroying the cell and releasing cellular components into the surrounding media. Further, these rotational devices are required to use rotating seals to seal the fluid pathways as they transition from a non-rotating to a rotating pathway. The frictional losses in this rotating seal also contribute to particle damage via excessive heat and shear forces.